1. Field of the Invention
The present invention relates to a numerical control device that controls a machine tool, and in particular, a numerical control device that speeds up a reversing operation of a machine tool.
2. Description of the Related Art
In a conventional operation for reversing the direction of movement using a machine tool, positioning accuracy when reversing is ensured by starting a post-reverse movement command (a movement command that is subsequent to a pre-reverse movement command) when the servo delay amount of the pre-reverse movement command has become equal to or lower than the in-position width (required accuracy), that is, within the margin of the predetermined error, when reversing (see Japanese Examined Patent Publication No. H7-16849).
Furthermore, in order to speed up a reversing operation, feed-forward control is used to set the servo delay amount to substantially zero, and the post-reverse movement command is started (overlapped), when the remaining amount of movement of the pre-reverse movement command has become equal to or lower than the in-position width (required accuracy) when reversing, thereby speeding up the reversing operation (see Japanese Patent Application Publication No. H11-39017 and Japanese Patent Application Publication No. 2009-282829).
However, in general, an acceleration and deceleration is applied to movement commands, and when reversing, due to the combination of the acceleration/deceleration of the pre-reverse movement command and the acceleration/deceleration of the post-reverse movement command, the timing at which the final combined movement command is reversed is delayed with respect to the start of the post-reverse movement command. Therefore, in the prior art, the actual accuracy when reversing is even better than the in-position width (required accuracy), but the cycle time is slowed accordingly.